Foam-backed pressure-sensitive adhesive tapes are used in a wide variety of applications. Some such tapes have a pressure-sensitive adhesive layer on each surface and may be used for mounting objects such as pictures on walls or plastic body side molding on automobiles. Other such tapes have only one adhesive layer. For example, a single-adhesive layer may function to position the foam backing as a cushioning gasket for an automobile window which is sealed by fastening a metal strip to the window frame. Most such applications require the foam backing to have both good compressibility and good resilience. For good compressibility, the foam should have an open-cell structure.
The backing of one such pressure-sensitive adhesive tape is a polyurethane foam, as disclosed in Canadian Pat. No. 747,341, but polyurethane foams tend to swell excessively in contact with oils such as gasoline, especially when of open-cell structure. Open-cell polyurethane foams tend to wick both gasoline and water and, in automotive use, may carry such liquids into the interior of the vehicle. Hence, tapes of the Canadian patent have been put to little or no exterior automotive use.
Vinyl foams have rather good resistance to gasoline and water and are used as backings in pressure-sensitive adhesive tapes for automotive use even though they tend to be of closed-cell structure and hence of limited compressibility. However, the plasticizers which are essential to their compressibility and resilience tend to migrate into the adhesive layers, eventually rendering them soft and pasty and destroying their holding power. The plasticizer migration problem becomes especially severe if the plasticizer level is increased in an effort to improve the limited compressibility of the foam.
Neoprene foams also offer good resistance to gasoline and water, but pressure-sensitive adhesive tapes made therewith are relatively expensive. These tend to have closed-cell structure so that it is difficult to attain the degree of compressibility which is generally desired for automotive applications.
Polyethylene foams are less expensive but also tend to have poor compressibility due to closed-cell structure. They exhibit less resistance to heat than do the aforementioned foams.